Some of the primary sources of industrial air pollution today include particulate matter produced from the combustion of fossil fuels, engine exhaust gases, and various chemical processes. An electrostatic precipitator provides an efficient way to eliminate or reduce particulate matter pollution produced during such processes. The electrostatic precipitator generates a strong electrical field that is applied to process combustion gases/products passing out an exhaust stack. Basically, the strong electric field charges any particulate matter discharged along with the combustion gases. These charged particles may then be easily collected electrically before exiting the exhaust stack and are thus prevented from polluting the atmosphere. In this manner, electrostatic precipitators play a valuable role in helping to reduce air pollution.
A conventional single-phase power supply for an electrostatic precipitator characteristically includes an alternating current voltage source of 380 to 600 volts having a frequency of either 50 or 60 Hertz. Typically, silicon-controlled rectifiers (SCRs), which may be controlled using a conventional automatic voltage control circuit device, are used to manage the amount of power and modulate the time that an alternating current input is provided to the input of a transformer and a full-wave bridge rectifier (called a TR set). The full-wave bridge rectifier converts the alternating current from the output of the transformer to a pulsating direct current and also doubles the alternating current frequency to either 100 or 120 Hertz, respectively. The high-voltage direct-current output produced is then provided to the electrostatic precipitator device. Typically, a low pass filter in the form, of a current limiting choke coil/reactance device such as an inductor and/or resistor is electrically connected in series between the silicon-controlled rectifiers and the input to the transformer for limiting the high frequency energy and shaping the output voltage waveform.
The electrostatic precipitator essentially operates as a big capacitor that has two conductors separated by an insulator. The precipitator discharge electrodes and collecting plates form the two conductors and the exhaust gas that is being cleaned acts as the insulator. Basically, the electrostatic precipitator performs two functions: the first is that it functions as a load on the power supply so that a corona discharge current between the discharge electrodes and collecting plates can be used to charge/collect particles; and the second is that it functions as a low pass filter. Since the capacitance of this low pass filter is of a relatively low value, the voltage waveform of the electrostatic precipitator has a significant amount of ripple voltage.
During operation, one phenomenon that can limit the electrical energization of the electrostatic precipitator is sparking. Sparking occurs when the gas that is being treated in the exhaust stack has a localized breakdown so that there is a rapid rise in electrical current with an associated decrease in voltage. Consequently, instead of having a corona current distributed evenly across an entire charge field volume within the electrostatic precipitator, there is a high amplitude spark that funnels all of the available current through one path across the exhaust gas rather than innumerable coronal discharge paths dispersed over a large area of the exhaust gas. Sparking can cause damage to the internal components of the electrostatic precipitator as well as disrupt the entire operation of the electrostatic precipitator. Therefore, an automatic voltage control circuit device is used to interrupt power once a spark is sensed. The current limiting reactance device then acts as a low pass filter to cut off delivery of any potentially damaging high frequency energy to the transformer. During this brief quench period, the current dissipates through this localized path of electrical conduction until the spark is extinguished and then the voltage is reapplied.
Therefore, to improve particle collection efficiency, it is necessary that the ripple voltage in the electrostatic precipitator be reduced. This is important since the presence of a ripple voltage results in a peak value of the voltage waveform for the electrostatic precipitator that is greater than the average value of the voltage waveform for the electrostatic precipitator. Therefore, since the peak value of the voltage waveform for the electrostatic precipitator must not exceed the breakdown or sparking voltage level due to the problems associated with sparking described above, the average voltage for operating the electrostatic precipitator must be kept at a lower level. Unfortunately, this lower level of average voltage adversely affects the particle collection efficiency of the electrostatic precipitator.
One method of accomplishing a reduction in ripple voltage involves using a pulsating direct current voltage mechanism that is operable to receive power from a single-phase alternating current voltage source along with a spiral wound filter capacitor in an arrangement where the pulsating direct current voltage mechanism is electrically connected in parallel to the spiral wound filter capacitor and the spiral wound filter capacitor is electrically connected in parallel to the electrostatic precipitator. An example circuit diagram of this type of prior art electrostatic precipitator is illustrated in FIG. 1 and discussed in detail in U.S. Pat. Nos. 6,839,251 and 6,611,440. As shown by FIG. 1, at least one spiral wound filter capacitor 62 is connected electrically in parallel with electrostatic precipitator 66 and acts to reduce voltage ripple and reshape the voltage waveform applied to the electrostatic precipitator so that when utilizing a single phase power supply the minimum value, average value and peak value of the applied voltage waveform are substantially the same. The use of one or more spiral wound filter capacitors 62 in this manner has the advantage of decreasing potentially damaging sparking currents and attenuating normal corona current.
Conventionally, the above described high voltage electrical components required for this type of electrostatic precipitator are not manufactured and housed all together in a single common enclosure. In fact, all of the components together occupy a significant amount of space and consequently impose significant space and footprint requirements for an installation. Unfortunately, locations in which such electrostatic precipitators and their associated voltage controlling electronics are typically used suffer from a dearth of available installation space. Accordingly, there is great need for an electrostatic precipitator system having a housing arrangement that encloses all or most of the above electrical components within a single compact housing that is safe, reliable, easy to install, occupies a relatively small volume and spatial footprint, is cost effective and provides sufficient and efficient heat dissipation for all of the housed components.